Out-of-state retailers exceeding $100,000 of sales or 200 transactions delivered into California will be required to collect California use taxes on their sales. The new use tax collection requirement is not retroactive and applies only to sales made on and after April 1, 2019.
Retailers who are already required to be registered to collect California use tax prior to April 1, 2019 will see no change in their registration obligations; retailers with a physical presence in California are still generally required to be registered with the CDTFA.
Retailers meeting the thresholds in a single district will also be responsible for collecting the use tax in that district. These voter-approved taxes are used to fund local services.
Taxpayer assistance is available at https://www.cdtfa.ca.gov/industry/wayfair.htm